Ultrasonic delay line

ABSTRACT

An ultrasonic delay line having an ultrasonic beam path with a plurality, preferably seven, reflection points, and comprising a body of lead silicate glass and a transmitting transducer and a receiving transducer. The body has top and bottom major surfaces substantially parallel to each other, first and second side surfaces which are substantially rectangular in shape and substantially at right angles to the top and bottom major surfaces, a third side surface substantially at a right angle to both the top major surface and the first side surface, a fourth side surface which is substantially at an angle of 135* to the first side surface and supporting either the transmitting transducer or the receiving transducer thereon, and a fifth side surface substantially at an angle of 135* to the second side surface and supporting the other of the transmitting and the receiving transducers thereon. In the preferred form, the medium has a shape such that the length of the first and second side surfaces is about three times the length of the third side surface. The medium may have, at a portion adjacent the ultrasonic beam path, at least one hole and at least one diffusion layer zone which has a lower mechanical Q than that of the ultrasonic beam path, and said hole may have an inner wall provided with an ultrasonic adsorber.

United States Kasahara et a1.

atent 1 Mar. 19, 1974 Masanari Mikoda; llsao Uerio, all of Osaka, Japan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan [22] Filed: May 15, 1972 [21] App]. No.: 253,116

[30] Foreign Application Priority Data May 14. 1971 Japan 46-32849 Mar. 6, 1972 Japan 47-23371 [52] US. Cl. 333/30 R, 333/72 [51] Int. Cl. H03h 9/30 [58] Field of Search 333/30 R, 7l-72 [56] References Cited UNITED STATES PATENTS 2,922,966 l/l960 Mortley 333/30 R 3,296,561 l/l967 Polucci 333/30 R 2.859.415 11/1958 Fagen 333/30 R 2,839.73] 6/1958 McSkimin.... 333/30 R 3.131.459 5/1964 Allen 333/30 R 3.247.473 4/1966 Allen 333/30 R 3.680.008 7/1972 Yamamoto 333/30 R 3.671.887 6/1972 Gibson 333/30 R FOREIGN PATENTS OR APPLICATIONS 116.769 5/1969 Norway 333/30 R OTHER PUBLICATIONS Brockelsby et al. Ultrasonic Delay Lines Illiffe Books Ltd. London 1963, TK7872D4B7; pp. 1 18-120 Primary ExaminerRudolph V. Rolinec Assistant Examiner-Marvin Nussbaum Attorney, Agent, or FirmWenderoth, Lind & Ponack [5 7 ABSTRACT An ultrasonic delay line having an ultrasonic beam path with a plurality, preferably seven, reflection points, and comprising a body of lead silicate glass and a transmitting transducer and a receiving transducer. The body has top and bottom major surfaces substantially parallel to each other, first and second side surfaces which are substantially rectangular in shape and substantially at right angles to the top and bottom major surfaces, a third side surface substantially at a right angle to both the top major surface and the first side surface, a fourth side surface which is substantially at an angle of 135 to the first side surface and supporting either the transmitting transducer or the receiving transducer thereon, and a fifth side surface substantially at an angle of 135 to the second side surface and supporting'the other of the transmitting and the receiving transducers thereon. 1n the preferred form, the medium has a shape such that the length of the first and second side surfaces is about three times the length of the third side surface. The medium may have, at a portion adjacent the ultrasonic beam path, at least one hole and at least one diffusion layer zone which has a lower mechanical Q than that of the ultrasonic beam path, and said hole may have an inner wall provided with an ultrasonic adsorber.

10 Claims, 13 Drawing Figures PATENTED "AR 1 9 I974 SHEU 1 (IF 6 PAIENIEDHARIQIQH 3.759 57? SHEET 2 OF 6 ULTRASONIC DELAY LINE FIELD OF THE INVENTION This invention relates to an ultrasonic delay line, and more particularly to a multipath delay line.

Solid delay lines, particularly multipath delay lines, have assumed increasing importance in view of their prospective application to television cameras and receivers, other types of systems employing storage and operational devices, and so on.

DESCRIPTION OF THE PRIOR ART In order to impose a prescribed delay on an ultrasonic beam traversing a solid medium, it is often necessary to provide an extended path for the beam. In order to make the body of the medium compact, this path is folded into a limited space by multiple internal reflections of the beam in the medium. Bodies geometrically designed to provide such multiple internal reflections of the transmitted beam are known as multireflection delay lines.

Ultrasonic delay lines using shear and longitudinal waves in rods or plates of acoustic delay media, such as vitreous silica, have been found to operate over wide frequency bands and to have delay characteristics that are stable with respect to time and temperature.

Solid delay lines have been constructed in a wide variety of forms, and the simplest form is a straight bar of vitreous silica or a similar material with transducers located at the two ends of the bar. As for materials for such as acoustic delay line, there is used quartz, vitreous silica, polycrystalline ceramics, acoustically isotropic metals, and so on. Because the delay time of a solid delay line of this type is short and it is economical to use, solid delay lines have been formed in the shape of solid rectangular bodies with facets on two or more corners of the rectangle to support transmitting and receiving transducers thereon. A delay line of this type has a longer delay time for a small size and light weight as compared with a straight ultrasonic delay line, but it requires that the solid medium have an extremely accurate shape.

Other types of delay lines in the form of irregular polygons have been developed so as to increase further the delay time of the delay line without increasing its physical size. These polygonal delay lines require as many as five or more accurately shaped facets so as to reflect properly the ultrasonic energy. The accurate shaping of these facets requires a time consuming and extremely expensive procedure. Furthermore, the positions of these facets are so interrelated that an error in shaping one facet may destroy entirely the usefulness ofthe delay line.

BRIEF SUMMARY OF THE INVENTION An object of this invention is to provide an improved delay line characterized by a low level of unwanted signals.

Another object of this invention is to provide a delay line having a low level of unwanted signals, as well as a miniaturized size.

A further object of this invention is to provide a delay line which is easily constructed so as to ensure a low level of unwanted signals.

For a better understanding of this invention, reference will now be made to the following detailed description, which is to be read in conjunction with the accompanying drawing, in which:

FIG. 1 is a plan view of a delay line having an ultra sonic beam path with seven reflection points according to the present invention;

FIG. 2 is a perspective view of a delay line similar to that of FIG. 1 having holes therethrough;

FIG. 3 is a perspective view of a delay line similar to that of FIG. 1 having diffusion layer zones thereon;

FIG. 4 is a perspective view of a delay line similar to that of FIG. 1 having holes therein with diffusion layer zones on the inside surfaces thereof;

FIGS. 57 are perspective views similar to FIG. 2 showing delay lines having alternative shapes for the holes;

FIG. 8 is a perspective view of another delay line according to the present invention having holes therethrough;

FIG. 9 is a perspective view of another delay line, according to the present invention, similar to FIG. 8 and having an ultrasonic absorber or diffusion layer zones on the inner surfaces of the holes;

FIGS. 1012 are perspective views of delay lines similar to that of FIG. 9 having alternative shapes for the holes; and

FIG. 13 is a perspective view of still another delay line according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Before referring to the drawings in detail, it should be noted that common elements necessary for the proper operation of an ultrasonic delay line have been omitted, for simplicity, from the drawings. For instance, connection between the transducers and an apparatus in which the delay line is used is omitted.

The ultrasonic delay line according to the present invention has an ultrasonic beam path with a plurality of of reflection points and comprises a body of lead silicate glass and a transmitting and a receiving transducer, said body having top and bottom major surfaces substantially parallel to each other, first and second side surfaces which are substantially rectangular in shape and substantially at a right angle to said top and bottom major surfaces, a third side surface substantially at a right angle to both said top major surface and said first side surface, a fourth side surface substantially at an angle of to said first side surface and supporting either said transmitting or said receiving transducer, and a fifth side surface substantially at an angle of 135 to said second side surface and supporting the other of said transmitting and receiving transducers.

In a first preferred embodiment, the body has a shape such that the length of said first and second side surfaces is about three times as much as that of said third side surface, whereby the ultrasonic beam path has seven reflection points.

Even though said body has a slightly inclined first or second side surface, an ultrasonic beam arrives extremely near the center of said receiving transducer. Therefore, a small transducer can be used in a delay line with a small mass of medium. A delay line using a body with such a shape has a small size, and it has a low level of attenuation since ultrasonic beam energy can be converted certainly and effectively to electric energy thereby, and it also has a low level of unwanted I signals since the ultrasonic beam thereof cannot propagate along the same path as an incidentbeam after reflection to said receiving transducer.

In another preferred embodiment, said body can have, at a portion adjacent to said ultrasonic beam path, at least one hole. Said hole extends from said top major surface to said bottom major surface. An ultrasonic beam projected from within the body toward the surface defining said hole is reflected at random by said surface. Accordingly, an output electric signal at said receiving transducer has a low level of unwanted signals. Said hole may have against the surface defining the hole an ultrasonic absorber such as rubber, wax, cement, resin or glass. Said hole may have a shape such as a rectangle, a cross, or an asterisk. An ultrasonic delay line with a body which has a hole having an ultrasonic absorber therein or has a hole having the shape of a rectangle, a cross, or an asterisk has a lower level of unwanted signals than that of an ultrasonic delay line with-a body which has a hole having the shape of a circle without an ultrasonic absorber within the hole.

In a third preferred embodiment, said body may have, at a portion adjacent an ultrasonic beam path, at least one diffusion layer zone which has a lower mechanical quality factor Q than that of the medium containing said ultrasonic beam path.

Said diffusion layer zone on said body of lead silicate glass can be formed by a diffusion process of diffusing into the glass monovalent cations such as Ag, Na or Li. Said diffusion process can be enhanced by using lead silicate glass containing fluorine ions. A past including monovalent cations is applied to desired portions of the surfaces of said body of lead silicate glass containing fluorine ions. Preferably the paste includes phosphate glass, lead borosilicate glass, waterglass, resin, etc., including monovalent cations. The applied paste is fired at about 500C in air. Said monovalent cations diffuse into said body and along the surface of said body and make the mechanical Q of the material of the body lower. At the surface of the resultant diffusion layer zone formed as described above, the mechanical Q has a gradient which changes continuously from a minimum value at the center of said zone to a high value at the periphery of said zone.

There are two types of surfaces on which said diffusion layer zone can be provided on the body. That is, the diffusion layer zone can be formed on one of the above-described major or side surfaces of said body or on the inner wall of the holes formed in the body.

During the firing process, the desired cations such as Ag Na or Li can migrate into the medium forming the body so as to form said diffusion layer zones. Preferred firing times have been found to be more than hours. Further, the cooling cycle for the firing is important because the cooling rate is known to affect the acoustic properties of the glass medium. In said process, the preferred cooling rate is about 5C/hour. The thickness of said diffusion layer zones can be controlled by the firing temperature and firing time.

Referring to FIG. 1, which shows one form of the first preferred embodiment, a body 11 of lead silicate glass has a substantially rectangular shape having a point at one end. Said body 11 has a top major surface 12 and a bottom major surface (not visible in the FIG.) which are substantially parallel to each other. A first side surface 14 and a second side surface 15, which are substantially parallel to each other and rectangular in shape, are substantially at right angles to both said top major surface 12 and said bottom major surface. A third side surface 16 having a rectangular shape is substantially at a right angle to both said top major surface 12 and said first side surface 14. A fourth side surface 17 and a fifth side surface 18 are substantially at an angle of to said first side surface 14 and said second side surface 15, respectively. A transmitting transducer 19 and a receiving transducer 20 are adhered to said fourth side surface 17 and said fifth side surface 18, respectively, by any available and suitable method.

When said body 11 has a shape such that the length of said top major surface 12 is about three times the width of said top major surface 12, said medium has seven reflection points, as shown in FIG. 1. An input electric signal is converted into an ultrasonic beam by said transmitting transducer 19. An ultrasonic beam radiated from said transmitting transducer 19 propagates along a beam path 21 and arrives at a reflection point 22 of said second side surface 15. Said ultrasonic beam then propagates along a beam path 23. Said ultrasonic beam propagates successively in the order of said second side surface 15, said first side surface 14, said second side surface 15, said third side surface 16, said first side surface 14, said second side surface 15, and said first side surface 14, along beam paths 23, 24, 25, 26, 27 and 28. Then said ultrasonic beam arrives at point 30 of said receiving transducer 20 adhered on said fifth side surface 18 at a right angle thereto along a beam path 29.

When said first side surface 14 is inclined to said second side surface 15 at an angle of 0, said body 11 has a first side surface 31 in place of said first side surface 14. An ultrasonic beam which has reflected at said inclined first side surface 31, after first being reflected from said second side surface 15, propagates not along said beam path 24, but along a beam path 32 which is inclined at an angle of 20 from said beam path 24. Said ultrasonic beam reflected at said inclined first side surface 31 propagates successively in the order of said second side surface 15, said third side surface 16, said inclined first side surface 31, said second side surface 15 and said inclined first side surface 31 along beam paths 32, 33, 34, 35 and 36. Then said ultrasonic beam reflected at said inclined first side surface 31 arrives at a point 38 of said receiving transducer 20 adhered on said fifth side surface 18 along a beam path 37. Said point 38 is very near to said point 30, and the difference of said incident beam angles between said beam path 37 and said beam path 29 relative to said receiving transducer 20 is only 0 degrees. Therefore, said ultrasonic beam is projected on the center of said receiving transducer 20, rather than missing said receiving transducer 20, and ultrasonic beam energy can be converted certainly and effectively to electric energy, although a miniaturized receiving transducer and a miniaturized body are used. Furthermore, an unwanted signal which is found at a time three times the delay time is hardly noticible because an ultrasonic beam reflected at said.

point 38 cannot propagate along the same paty as said incident beam path 37 to said receiving transducer 20, because of the oblique incidence of said beam to said receiving transducer 20.

Referring to FIG. 2, a body 41 of lead silicate glass has a thin rectangular shape having a point at one end. Said body 41 has a top major surface 42 and a bottom major surface 43 which are substantially parallel to each other. A first side surface 44 and a second side surface 45, each substantially rectangular in shape, are substantially at right angles to both said top major surface 42 and said bottom major surface 43. A third side surface 46 substantially rectangular in shape is substantially at a right angle to both said top major surface 42 and said first side surface 44. A fourth side surface 47 and a fifth side surface 48 are substantially at an angle of 135 to said first side surface 44 and said second side surface 45, respectively. A transmitting transducer 49 and a receiving transducer 50 are adhered to said fourth side surface 47 and said fifth side surface 48, respectively, by any available and suitable method. Said body 41 has, at three portions 51, 52 and 53 adjacent an ultrasonic beam path 54, three circular holes 55, 56 and 57 extending from said top major surface 42 to said bottom major surface 43. Said transmitting transducer 49 is polarized in a direction parallel to both said top major surface 42 and said fourth side surface 47. Said receiving transducer 50 is polarized in a direction parallel to both said top major surface 42 and said fifth side surface 48.

When said body 41 has a shape such that the length of said first side surface 44 is about three times the length of said third side surface 46, said body 41 has seven reflection points and reflects said ultrasonic beam along a path 54 as shown in FIG. 2. An input electric signal is converted into an ultrasonic beam by said transmitting transducer 49. Said ultrasonic beam propagates along said beam path 54, as shown in FIG. 2. A beam projected from within the body on the surface defining one of said holes 55, 56 and 57 is refiected at random by said surface defining one of said holes 55, 56 and 57. Accordingly, an output electric signal at said receiving transducer 50 has a low level of unwanted signals.

Referring to FIG. 3, a body 61 of lead silicate glass has a thin rectangular shape having a point at one end. Said body 61 has a top major surface 62 and a bottom major surface 63 which are substantially parallel to each other. A first side surface 64 and a second side surface 65, each substantially rectangular in shape, are substantially at right angles to both said top major surface 62 and said bottom major surface 63. A third surface 66 substantially rectangular in shape is substantially at a right angle to both said top major surface 62 and said first side surface 64. A fourth side surface 67 and a fifth side surface 68 are substantially at an angle of 135 to said first side surface 64 and said second side surface 65, respectively. A transmitting transducer 69 and a receiving transducer 70 are adhered to said fourth side surface 67 and said fifth side surface 68, respectively, by any available and suitable method. Each of said first side surface 64 and second side surface 65 is provided, respectively, with four diffusion layer zones 71, 72, 73 and 74 by the method described hereinbefore. The four diffusion layer zones on said first side surface 64 are opposed to the corresponding four diffusion layer zones on said second side surface 65. Said transmitting tranducer 69 is polarized in a direction parallel to both said top major surface 62 and said fourth side surface 67. Said receiving transducer 70 is polarized in a direction parallel to both said top major surface 62 and said fifth side surface 68.

When said body 61 has a shape such that the length of said first side surface 64 is about three times the length of said third side surface 66, said body 61 has seven reflection points as shown in FIG. 3. An input electric signal is converted into an ultrasonic beam by said transmitting transducer 69. Said ultrasonic beam propagates along a beam path 75 as shown in FIG. 3. The seven reflection points have no diffusion layer zones and have a high mechanical quality factor Q. A beam projected on said diffusion layer zones 71, 72, 73 and 74 is absorbed by said diffusion layer zones 71, 72, 73 and 74. Accordingly, an output eelectric signal at said receiving transducer 70 has a low level of unwanted signals.

Referring to FIG. 4, a body 81 of lead silicate glass has a thin rectangular shape having a point at one end. Said body 81 has a top major surface 82 and a bottom major surface 83 which are substantially parallel to each other. A first side surface 84 and a second side surface 85, each substantially rectangular in shape, are substantially at right angles to both said top major surface 82 and said bottom major surface 83. A third side surface 86 substantially rectangular in shape is substantially at a right angle to both said top major surface 82 and said first side surface 84. A fourth side surface 87 and a fifth side surface 88 are substantially at an angle of 135 to said first side surface 84 and said second side surface 85, respectively. A transmitting transducer 89 and a receiving transducer 90 are adhered to said fourth side surface 87 and said fifth side surface 88, respectively, by any available and suitable method. Said body 81 has, at three portions 91, 92 and 93 adjacent an ultrasonic beam path 94, three holes 95, 96 and 97 extending from said top major surface 82 to said bottom major surface 84. Said holes 95, 96, 97 have the surfaces defining the holes provided with diffusion layer zones 98, 99 and 100 by the method described hereinbefore, respectively. Said transmitting transducer 89 is polarized in a direction parallel to both said top major surface 82 and said fourth side surface 87. Said receiving transducer 90 is polarized in a direction parallel to both said top major surface 82 and said fifth side surface 88.

When said body 81 has a shape such that the length of said first side surface 84 is about three times the length of said third side surface 86, said body 81 has seven reflection points and reflects said ultrasonic beam along a path 94, as shown in FIG. 4. An input electric signal is converted into an ultrasonic beam by said transmitting transducer 89. Said ultrasonic beam propagates along said beam path 94 as shown in FIG. 4. A beam projected on said diffusion layer zones 98, 99 and 100 is absorbed by said diffusion layer zones 98, 99 and 100, respectively. Accordingly, an output electric signal at said receiving transducer 90 has a low level of unwanted signals.

A delay line having a delay time of about 64 usec was made by using a medium having a composition of 72% SiO 15.5% PbO, 3.2% PbF 7.0% K 0, 1.5% A1 0 and 0.8% AS203, all percentages being mole percent.

The ssaytistfififialawragamaasms 'uiemajar' surface 12 was 17 mm in width, and the first side surface 14 was 51 mm in length and 1 mm in width. In experiments, it was found that a delay line using a body with an inclined first side surface at an angle 6 less than 1 has a low level of attenuation the same as a delay line having a body with the first and the second side surfaces parallel to each other.

The resultant delay line made as described above had 10 dB of attenuation and -20 dB of unwanted signals. On the other hand, a delay line which had a body with the top major surface 34 mm in widht and a first side surface 48 mm in length and 1 mm in width had a similar delay time to the above delay line and had 10 dB of attenuation and 10 dB of unwanted signals.

When said first-mentioned delay line having seven reflection points was provided with three holes, as shown in FIG. 2, the resultant delay line had 26 dB of unwanted signals. In this case, the holes had a diameter of mm.

When said firstmentioned delay line with seven reflection points and three holes further had epoxy resin as an ultrasonic absorber in said holes, the resultant delay line had 32 dB of unwanted signals.

When said first-mentioned delay line having seven reflection points was further provided with four diffusion layer zones at four portions adjacent the ultrasonic beam path as shown in FIG. 3 on said first and second side surfaces, respectively, the resultant delay line had 26 dB of unwanted signals. In this case, said eight diffusion layer zones were formed by firing a paste having a composition of 100g of glass frit, 3g of cellulose acetate butylate, 17g of terpineol and lg of surface active agent, said glass frit composition being 7.7% SiO 35.3% Na O, 6.9% PbO and 50.1% B 0 all percentages being mole percent, at 500C for hours.

Further, when said delay line having seven reflection points and eight diffusion layer zones was further provided with three holes having diffusion layer zones therein shown in FIG. 4, the resultant delay line had -32 dB of unwanted signals. In this case, the holes had a diameter of 5 mm and the diffusion process was similar to that of the above delay line.

Further, when said delay line having seven reflection points and eight diffusion layer zones was further provided with three holes having the shape of either a rectangle, a cross or an asterisk instead of a circle having said diffusion layer zones therein, as shown in FIG. 4, the resultant delay line had 36 dB of unwanted signals, respectively. In these cases, the hole in the shape of a rectangle had a dimension parallel to the top major surface which was 5 mm in length and was 1 mm in width, while the hole in the shape of a cross had two bars which were 5 mm in length and 1 mm in width and were at right angles to each other, and the hole in the shape of an asterisk had a size similar to that of a circle having a diameter of 5 mm.

Said body can have a sixth side surface and a seventh side surface which are parallel to said fourth side surface 17 and said fifth side surface 18, respectively. Said sixth and seventh side surfaces are effective to suppress unwanted signals when said sixth and seventh side surfaces are positioned so as not to interfere with said ultrasonic beam path. A delay line with said sixth and seventh side surfaces showed a level of unwanted signals lower by 5 dB than a delay line without said sixth and said seventh side surfaces.

When a body has seven or more reflection points along an ultrasonic beam path, the electrical characteristics of the delay line depend on the roughness of the top and bottom major surfaces of said body. Such a body was prepared having a size as described above, and said major surfaces were ground using SiC powder.

When the roughness of said major surfaces of said body with seven reflection points as shown in FIG. 1 was one tenth, one-twentieth, one-thirtyfifth and onefiftieth of the wave length of the ultrasonic wave along said beam path, the electrical characteristics of said delay line were attenuation of 14 dB, 12 dB, 10 dB and 1.2 MHz, 1.6 MHz, 2.0 MHz and 2.4 MHz in bandwidth under 3 dB from minimum attenuation, respectively. Accordingly, a body with said major surfaces which have a roughness less than one-twentieth of the wave length of the ultrasonic wave is extremely effective as a delay line for use in a device such as a PAL color television receiver.

Referring to FIG. 8, there is shown a second preferred embodiment which is similar to that of FIG. 2, except for the size, which is not limited to that necessary to give to the ultrasonic beam path seven reflection points. A body 211 of lead silicate glass has a thin substantially rectangular shape having a point at one end. Said body 211 has a top major surface 212 and a bottom major surface 213 which are substantially parallel to each other. A first side surface 218 and a second side surface 219, which are substantially parallel to each other and rectangular in shape, are substantially at right angles to said top major surface 212 and said bottom major surface 213. A third side surface 220 having a rectangular shape is substantially at a right angle to both said top major surface 212 and said first side surface 218. A fourth side surface 214 and a fifth side surface 215 are substantially at a right angle to said top major surface 212, and are substantially at an angle of to said first side surface 218 and said second side surface 219, respectively. A transmitting transducer 216 and a receiving transducer 217 are adhered to said fourth side surface 214 and said fifth side surface 215, respectively, by any available and suitable method. Said transmitting transducer 216 is polarized in a direction parallel to both said top major surface 212 and said fifth side surface 215. Said body 211 has, at two portions 221 and 222 adjacent to an ultrasonic beam path 223, two circular holes 224 and 225 extending from said top major surface 212 to said bottom major surface 213.

When said body 211 has a shape such that the length of said first side surface 218 is about two times the length of said third side surface 220, said body 211 has five reflection points and reflects said ultrasonic beam along path 223, as shown in FIG. 8. An input electric signal is converted into an ultrasonic beam by said transmitting transducer 216. Said ultrasonic beam propagates along said beam path 223, as shown in FIG. 8. A beam projected from within the body on the surface defining one of said holes 224 and 225 is reflected at randon by the surface defining the hole and is reduced after several reflections. Accordingly, an output electric signal at said receiving transducer 217 has a low level of unwanted signals.

Referring to FIG. 9, a body 231 of lead silicate glass has a thin rectangular shape having a point at one end. Said body 231 has a top major surface 232 and a bottom major surface 233 which are substantially parallel to each other. A first side surface 238 and a second side surface 239, each substantially rectangular in shape, are substantially at right angles to said top major surface 232 and said bottom major surface 233. A third side surface 240 substantially rectangular in shape is substantially at a right angle to both said top major surface 232 and said first side surface 238. A fourth side surface 234 and a fifth side surface 235 are substantially at a right angle to said top major surface 232, and are substantially at an angle of 135 to said first side surface 238 and said second side surface 239, respectively. A transmitting transducer 236 and a receiving transducer 237 are adhered to said fourth side surface 234 and said fifth side surface 235, respectively, by any available and suitable method. Said transmitting transducer 236 is polarized in a direction parallel to both said top major surface 232 and said fourth side surface 234. Said receiving transducer 237 is polarized in a direction parallel to both said top major surface 232 and said fifth side surface 235. Said body 231 has, at two portions 241 and 242 adjacent to an ultrasonic beam path 243, two holes 244 and 245 extending from said top major surface 232 and said bottom major surface 233. Said holes 244 and 245 have the surfaces defining the holes provided with layers 246 and 247 of an ultrasonic absorber, respectively.

When said body 231 has a shape such that a length of said first side surface 238 is about two times the length of said third side surface 240, said body 231 has five reflection points and reflects said ultrasonic beam along a path 243 as shown in FIG. 9. An input electric signal is converted into an ultrasonic beam by said transmitting transducer 236. Said ultrasonic beam propagates along said beam path 243 as shown in FIG. 9. A beam projected on the surfaces defining said holes 244 and 245 is absorbed by said ultrasonic absorbing layers 246 and 247 of said holes 244 and 245, respectively. Accordingly, an output electric signal at said receiving transducer 237 has a low level of unwanted signals.

A delay line having a delay time of about 64 usec was made by using a medium having a composition of 72% SiO 15.5% PbO, 3.2% PbF 7.0% K 0, 1.5% A1 and 0.8% As O all percentages being mole percent. The body had the following dimensions: the top major surface 212 was 24 mm in width, the first side surface 218 was 48 mm in length and 1 mm in width. Said body had, at two portions adjacent to the ultrasonic beam path, two circular holes extending from said top major surface 212 to said bottom major surface 213. The resultant delay line had l6 dB of unwanted signals. On the other hand, a delay line which was similar in size to the above delay line and had no holes had -10 dB of unwanted signals. In this case, the holes had a diameter of 8.5 mm.

When said firstmentioned delay line having two holes had epoxy resin as an ultrasonic absorber in said holes as shown in FIG. 9, the resultant delay line had 22 dB of unwanted signals.

Further, when said delay line was provided with two holes which were in the shape of a rectangle 250, a cross 251 or an asterisk 252, as shown in FIGS. 10-12 and had epoxy resin in said holes as described above, the resultant dely lines had -27 dB of unwanted signals. In these cases, the rectangle had a dimension parallel to said top major surface 212 12 mm in length and 1 mm in width, while the hole in the shape of a cross had two rectangles which were 8.5 mm in length and 1 mm in width, and were at right angles to each other, and the hole in the shape of an asterisk has a size similar to that of a circle having a diameter of 8.5 mm.

Referring to FIG. 13, there is shown a third preferred embodiment which is similar to that of FIG. 3, except for the size, which is not limited to that necessary to give the ultrasonic beam path seven reflection points. A body 311 of lead silicate glass has a thin substantially rectangular shape having a point at one end. Said body 311 has a top major surface 312 and a bottom major surface 313 which are substantially parallel to each other. A first side surface 314 and second side surface 315, each of which are substantially rectangular in shape, are at substantially right angles to both of said top major surface 312 and said bottom major surface 313. A third side surface 316 having a rectangular shape is substantially at a right angle to both said top major surface 312 and said first side surface 314. A fourth side surface 317 and a fifth side surface 318 are substantially at a right angle to said top major surface 312 and are substantially at an angle of 135 to said first side surface 314 and said second side surface 315, respectively. A transmitting transducer 319 and a receiving transducer 320 are adhered to said fourth side surface 317 and said fifth side surface 318, respectively, by any available and suitable method. Each of said first side surface 314 and second side surface 315 is provided with three diffusion layers zones 322, 323 and 324 by the method described above. The three diffusion layer zones on said first side surface 314 are opposed to the corresponding diffusion layer zones on the second side surface 315, respectively. Said transmitting transducer 319 is polarized in a direction parallel to both said top major surface 312 and said fourth side surface 317. Said receiving transducer 320 is polarized in a direction parallel to both said top major surface 312 and said fifth side surface 318.

When said body 311 has a shape such that the length of said top major surface 312 is about two times the width of said top major surface 312, said body has five reflection points, as shown in FIG. 13. An input electric signal is converted into an ultrasonic beam by said transmitting transducer 319. Said ultrasonic beam propagates along a beam path 321 as shown in FIG. 13. There are no diffusion layer zones at the five reflection points and the reflection points have a high mechanical Q. A beam projected on the diffusion layer zones 322, 323 and 324 is absorbed by said diffusion layer zones. Accordingly, the output electric signal at said receiving transducer 320 has a low level of unwanted signals.

A delay line having a delay time of about 64 usec was made by using a medium having a composition of 72% SiO 15.5% PbO, 3.2% PbF 7.0% K 0, 1.5% A1 0 and 0.8% AS203, all percentages being mole percent. The body had the following dimensions: the top major surface 312 was 24 mm in width, and a first side surface 314 was 48 mm in length and 1 mm in width. Each of the first and second side surfaces 314 and 315 had three diffusion layer zones 10 mm in length and 1 mm in width. Said three diffusion layer zoneswere formed by firing a paste having a composition of g of glass frit, 3g of cellulose acetate butylate, 17g of terpineol and 1g of surface active agent, asaid glass frit composition being 7.7% SiO 35.3% Na O, 6.9% Pb() and 50.1% B 0 all percentages being mole percent at 500C for 10 hours. The resultant delay line made as described above had 26 dB of unwanted signals. On the other hand, a delay line which was similar in size to the above delay line but had no diffusion layer zones had 10 dB of unwanted signals.

When a like delay line having six diffusion layer zones was also provided with two holes having diffusion layer zones therein, as shown in FIG. 9, the resultant delay line had 32 dB of unwanted signals. In this case, the holes had a diameter of 8.5 mm and the diffusion process was similar to that described hereinbefore.

Further, when such a delay line having six diffusion layer zones was provided with two holes having the shape of a rectangle, a cross or an asterisk, as shown in FIGS. -12, instead of a circle, having a diffusion layer on the inside thereof, the resultant delay line had -36 dB of unwanted signals, respectively. In these cases, the rectangle had a dimension of 12 mm parallel to the top major surface and was 1 mm in width, while the hole in the shape of the cross was formed of two rectangles 8.5 mm in length and 1 mm in width which were at right angles to each other, and the hole in the shape of the asterisk had a size similar to that ofa circle having a diameter of 8.5 mm.

It will be understood that, although a particular embodiment of this invention has been described in detail by way of illustrative example, this invention as herein set forth and as defined in the appended claims is not limited to structures of the specific form and dimensions indicated.

What is claimed is:

1. An ultrasonic delay line having an ultrasonic beam path therein with reflection points which comprises a body of lead silicate glass, a transmitting transducer and a receiving transducer, said body having top and bottom major surfaces parallel to each other, first and second side surfaces each substantially rectangular in shape and being at substantially right angles to said top and bottom major surfaces, a third side surface substantially at a right angle to both said top major and bottom major surfaces and said first side surface, a fourth side surface at an angle of substantially 135 to said first side surface and having one of said transmitting and receiving transducers mounted thereon, and a fifth side surface at an angle of substantially 135 to said second side surface and having the other of said transmitting and receiving transducers mounted thereon, said body having, at a portion adjacent to said ultrasonic beam path, at least one diffusion layer zone which has a lower mechanical quality factor Q than the quality factor Q of the material of said body.

2. An ultrasonic delay line as claimed in claim 1 wherein said body has at least one diffusion layer zone on said first and second side surfaces between adjacent reflection points.

3. An ultrasonic delay line as claimed in claim 1 wherein said body has, at a portion adjacent to said ultrasonic beam path, at least one hole therethrough, the surface of said body defining said hole having thereon said diffusion layer zone.

4. An ultrasonic delay line as claimed in claim 3 wherein said hole has a shape taken from the geometric figures consisting of a circle, a rectangle, a cross and an asterisk.

5. An ultrasonic delay line having an ultrasonic beam path therein with seven reflection points which comprises a body of lead silicate glass, a transmitting transducer and a receiving transducer, said body having top and bottom major surfaces substantially parallel to each other, first and second side surfaces each substantially rectangular in shape and being at substantially right angles to both said top and bottom major surfaces, a third side surface at substantially a right angle to both said top major surface and said first side surface, a fourth side surface at an angle of substantially to said first side surface and having one of said transmitting and receiving transducers mounted thereon, and a fifth side surface at an angle of substantially 135 to said second side surface and having the other of said transmitting and receiving transducers mounted thereon, said body having a shape such that the length of said first and second side surfaces is about three times the length of said third side surface.

6. An ultrasonic delay line as claimed in claim 5, wherein said body has, at a portion adjacent to said ultrasonic beam path, at least one hole therethrough, said hole having on the surface thereof a diffusion layer zone which has a lower mechanical quality factor 0 than the quality factor Q of the material of the body around said hole through which said ultrasonic beam path extends.

7. An ultrasonic delay line as claimed in claim 5, wherein said body has, at said first and second side surfaces, at least one diffusion layer zone between adjacent reflection points of said ultrasonic beam path, said diffusion layer zone having a lower mechanical quality factor Q than the quality factor Q of the material of said body at said reflection points.

8. An ultrasonic delay line as claimed in claim 6 wherein the surface of said body defining said hole has thereon an ultrasonic absorber of a material selected from a group consisting of rubber, wax, cement, resin and glass.

9. An ultrasonic delay line as claimed in claim 6 wherein said hole has a shape taken from the geometric figures consisting of a circle, a rectangle, a cross and an asterisk.

10. An ultrasonic delay line as claimed in claim 5 wherein said top and bottom major surfaces have a roughness less than one twentieth the wave length of the ultrasonic wave projected along said beam path. 

1. An ultrasonic delay line having an ultrasonic beam path therein with reflection points which comprises a body of lead silicate glass, a transmitting transducer and a receiving transducer, said body having top and bottom major surfaces parallel to each other, first and second side surfaces each substantially rectangular in shape and being at substantially right angles to said top and bottom major surfaces, a third side surface substantially at a right angle to both said top major and bottom major surfaces and said first side surface, a fourth side surface at an angle of substantially 135* to said first side surface and haVing one of said transmitting and receiving transducers mounted thereon, and a fifth side surface at an angle of substantially 135* to said second side surface and having the other of said transmitting and receiving transducers mounted thereon, said body having, at a portion adjacent to said ultrasonic beam path, at least one diffusion layer zone which has a lower mechanical quality factor Q than the quality factor Q of the material of said body.
 2. An ultrasonic delay line as claimed in claim 1 wherein said body has at least one diffusion layer zone on said first and second side surfaces between adjacent reflection points.
 3. An ultrasonic delay line as claimed in claim 1 wherein said body has, at a portion adjacent to said ultrasonic beam path, at least one hole therethrough, the surface of said body defining said hole having thereon said diffusion layer zone.
 4. An ultrasonic delay line as claimed in claim 3 wherein said hole has a shape taken from the geometric figures consisting of a circle, a rectangle, a cross and an asterisk.
 5. An ultrasonic delay line having an ultrasonic beam path therein with seven reflection points which comprises a body of lead silicate glass, a transmitting transducer and a receiving transducer, said body having top and bottom major surfaces substantially parallel to each other, first and second side surfaces each substantially rectangular in shape and being at substantially right angles to both said top and bottom major surfaces, a third side surface at substantially a right angle to both said top major surface and said first side surface, a fourth side surface at an angle of substantially 135* to said first side surface and having one of said transmitting and receiving transducers mounted thereon, and a fifth side surface at an angle of substantially 135* to said second side surface and having the other of said transmitting and receiving transducers mounted thereon, said body having a shape such that the length of said first and second side surfaces is about three times the length of said third side surface.
 6. An ultrasonic delay line as claimed in claim 5, wherein said body has, at a portion adjacent to said ultrasonic beam path, at least one hole therethrough, said hole having on the surface thereof a diffusion layer zone which has a lower mechanical quality factor Q than the quality factor Q of the material of the body around said hole through which said ultrasonic beam path extends.
 7. An ultrasonic delay line as claimed in claim 5, wherein said body has, at said first and second side surfaces, at least one diffusion layer zone between adjacent reflection points of said ultrasonic beam path, said diffusion layer zone having a lower mechanical quality factor Q than the quality factor Q of the material of said body at said reflection points.
 8. An ultrasonic delay line as claimed in claim 6 wherein the surface of said body defining said hole has thereon an ultrasonic absorber of a material selected from a group consisting of rubber, wax, cement, resin and glass.
 9. An ultrasonic delay line as claimed in claim 6 wherein said hole has a shape taken from the geometric figures consisting of a circle, a rectangle, a cross and an asterisk.
 10. An ultrasonic delay line as claimed in claim 5 wherein said top and bottom major surfaces have a roughness less than one twentieth the wave length of the ultrasonic wave projected along said beam path. 